1. Description of the Related Art
The present disclosure refers to a control device for a flyback converter.
2. Description of the Related Art
Flyback converters are known in the state of the art as DC to DC converters with a galvanic isolation between the input and the output. More precisely, the flyback converter is a buck-boost converter with the inductor split to form a transformer, so that the voltage ratios are multiplied with an additional advantage of isolation. The transformer includes a primary winding connected with the input of the converter and a secondary winding connected with the output of the converter.
A flyback converter can be used to supply LED diode chains.
Recently high brightness LEDs are becoming a prominent source of light and often have better efficiency and reliability when compared to that of conventional light sources. While LEDs can operate from an energy source as simple as a battery and resistor, most applications require an efficient energy source not only for the reduction of losses, but also for the lumen maintenance of the LED itself. For these reasons driving circuits for high brightness LEDs have been developed; these driving circuits assure a constant current to the LEDs.
Two of these circuits are the VIPer12A and VIPer22A developed by STMicroelectronics; they are integrated switching regulators capable of providing a constant current to the LEDs. VIPer12A and VIPer22A use typically secondary regulation for keeping the output current constant, that is the current of the LEDs, because it is necessary for proper LED driving. In fact the controller of the power switch of the flyback converter in VIPer12A and VIPer22A needs a feedback signal derived from the secondary side (the circuit part of the flyback converter that is coupled to the secondary winding of the transformer) to control the switch and to produce a constant output current. Secondary regulation also needs an optocoupler, several passive components, and an active component. If the output voltage is too high, for example higher than 36 V, it is even necessary to use additional secondary windings on the transformer to generate a proper supply voltage for secondary part as it is shown in the application notes AN2067 and AN1916 (documents AN2067 and AN1916 are available on the STMicroelectronics web site).
The main drawback for the circuits VIPer12A and VIPer22A is due to the use of numerous components with secondary regulation, which make them complex and increase the cost and size, as the use of the optocoupler to separate the feedback signal from secondary to primary side. Also, an additional secondary winding on the transformer is needed for high output voltage, higher than 36 V, to generate proper supply voltage for the secondary side.
In view of the state of the art, the present disclosure provides a control device for a flyback converter that has fewer components than the known circuits.